Tuesday, October 25, 2011

HAIs and resistant superbugs

Superbugs are common microbes that have been genetically modified to become multiple-drug-resistant strains. Bacteria have developed resistance to almost all existing antibiotics known today and this has been a major issue over the last few decades (Palanychamay and Kaliappan, 2010).
The prevalence of superbugs, such as vancomycin-resistant Staphylococcus aureus (VRSA) and methicillin-resistant Staphylococcus aureus (MRSA), is increasing at a rapid rate both in the hospital sector and in the community. Surveys revealed that resistance rates were higher in bacterial isolates derived from in-patients when compared with those from out-patients or from general practice (Shannon and French, 2004).
Multidrug resistance is worrisome since it corresponds to the addition of unrelated mechanisms of resistance that are difficult if not impossible to reverse once gathered in single genetic resistance structure (transposon, integron, plasmid), these latter structures contributing to co-selection of resistances (Nordmann et al., 2007).
The great genetic plasticity of bacteria has permitted the transfer of resistance genes on plasmids and integrons between bacterial species allowing an unprecedented dissemination of genes leading to broad-spectrum resistance (Gootz, 2006).
Recent evidence suggests that antibiotic resistance genes in human bacterial pathogens originate from a multitude of bacterial sources, indicating that the genomes of all bacteria can be considered as a single global gene pool into which most, if not all, bacteria can dip for genes necessary for survival (Bennett, 2008).
Causes of superbugs prevalence in HAIS:
It is notable that the majority of infection control problems in the hospital are due to increasingly resistant bacteria. It is important to reflect on the role that antibiotic use may have as a selecting force for evolution of these superbugs. Selecting force of antibiotics, combined with lapses in infection control techniques make from these resistant organisms resident flora in hospitals and lead to their spread from person to person (Gould, 2009).
A-Selective pressure of antibiotic use:
Current policies to shorten length of stay and curtail costs encourage empiric use, often of unnecessarily broad-spectrum antibiotics. Combination therapy is often used for a number of reasons including broadening spectrum to accommodate increasing antibiotic resistance. This over-use and sometimes misuse inevitably leads to evolution and spread of superbugs (Gould, 2009).
Evolution of antibiotic resistance is the result of two essential forces: variability (chance) and selection (necessity). Variability is created by random mutation; variants with a mutation in the antibiotic target become resistant. These variants are selected by antibiotic use and consequently they increase the frequency of resistance. If the variability (as in a hyper-mutable strain) increased or the intensity of selection (antibiotic hyper-consumption) increased, the result is more resistance (Baquero and Cantón, 2009).
Manual of Antibiotics: Method of Actions, Mechanisms of Resistance and Relations to Health Care associated Infections [Kindle Edition]